NCTM Standards: Represent and analyze mathematical situations and structures using algebraic symbols; Understand patterns, relations and functions
Activity 13: Do Opposites Attract?Added on 12/12/2007 |
Downloads: TI-73 PDF file |
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| ACTIVITY OVERVIEW In this activity we will:
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You might be familiar with adding numbers that have the same sign. You add them and the sign remains the same. If you lose $20 and then later lose another $20, you’ve lost $40 altogether. This would be the same as -20 + -20 and would = -40. |
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What happens when you are combining numbers with opposite signs? Let’s use the Number Line application to investigate this situation. On your TI-73, press the  key and select NUMLINE. Press  twice and select 1: Number Line. Press  . |
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| HINT So your window will show the entire problem, press the  key and set your minimum to -20 and your maximum to 20. |
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| Enter -5 +9 into the screen and press . |
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Press the up arrow key ( ) three times to get to the 0 on the equation. Use the up and down arrow keys to move through the problem to see where each number takes you on the number line. Where are you on the number line in this screen? Record this in your notebook. |
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Press  and select 1: YES to start a new problem. |
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Try these problems and think about where you will end on the number line. Do you think the order matters? If you are not sure, redo the problem by switching the two numbers. You can also arrow up to the problem and press the  key to remove the parts of the problem to start a new one. |
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| Have you come up with “theory” as to what happens when you add two differently signed numbers? If you have, write and test problems that have opposite signs in the problems but give the answers on the right. Write your problem after the answer once you have checked it. |
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| See if you can solve these problems with a number missing. Apply your “theory” to find the answer to make the problem correct. |
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